1. Field of the Invention
This invention relates to a method and an apparatus of treating photoresist materials applied on semiconductor wafer and, more particularly, to a method and an apparatus of treating the photoresist materials placed under a low atmospheric pressure employing ultraviolet irradiation.
2. Description of the Prior Art
As for the prior-art treatment of a photoresist employing ultraviolet irradiation, exposing the photoresist to ultraviolet radiation is utilized in a treatment in which a mask pattern is formed by exposing the photoresist applied on a semiconductor wafer, etc., and recently attention has been paid to the application of this method to particular treatments of photoresists such as baking photoresist materials.
The baking process is an intermediate between a process of forming a photoresist pattern by applying, exposing and developing the photoresist and a process of executing ion implantation, plasma-etching, etc. by using the photoresist pattern, and it is a heating process executed for improving the adhesiveness of the photoresist to a semiconductor substrate, heat-resistance, etc. While a reference of H. Hiraoka and J. Pacansky: J. Vac, Sci Tech. 19(1981), and U.S. application Ser. No. 923,504, abandoned have been made recently on a method in which ultraviolet rays are applied to the photoresist image after or during the baking process after development so as to enhance the heat-resistance and plasma-resistance of the photoresist through the baking process in a shorter time.
When a light having a high ultraviolet intensity, such as a radiant light from a microwave-excited electrodeless discharge lamp having a high ultraviolet radiation efficiency, is applied to the photoresist to expedite the treatment, however, a gas is generated from the photoresist, and this gas causes the formation of bubbles, deformation of a photoresist pattern and deformation of a photoresist film, such as exfoliation, rupture or roughening thereof, thus causing imperfections of a semiconductor element.
It can be supposed that the generation of this gas is caused by a rapid photochemical reaction of the light sensitive radicals of the photoresist, by the photochemical reaction of HMDS(hexamethyldisilazine), which is applied to a wafer as a preliminary treatment for the application of the photoresist, or an antireflection coating, etc. on the photoresist, by the photochemical reaction of an additive to the photoresist such as dyestuff, by the photochemical reaction of a solvent remaining in the photoresist, etc.
These photochemical reactions are advanced remarkably by a light having a wavelength 300 nm to 500 nm, and more particularly, by a light having a wavelength in the spectral response region of the photoresist. Accordingly, when a microwave-excited electrodeless discharge lamp radiating a light including these wavelength areas is employed, the intensity of light cannot be enhanced. In other words, this apparatus has a problem that it cannot perform a high-speed treatment.